1. Field of the Invention
The invention is directed to a method for the operation of an electrographic printer or copier, whereby a layer containing toner particles, referred to in brief as toner layer, is deposited on a toner acceptance surface under the influence of a force field. At least a part of the deposited toner particles is transferred onto a second toner acceptance surface under the influence of a second force field, the transferred toner particles forming a second layer thereon.
2. Description of the Related Art
Such a method is implemented in the developer unit that is set forth in European Patent EP 0 494 454 B1. Given this developer unit, the toner particles are electrically charged in a toner reservoir wherein a toner-air mixture is located and are subsequently deposited on the first toner acceptance surface that is grounded or provided with a potential, being deposited thereon as toner layer under the influence of an electrical force field. Due to the rotation of a developer drum whose generated surface forms the toner acceptance surface, the deposited toner particles are conducted past a development gap between the developer drum and a toner image carrier.
The second toner acceptance surface is formed by the generated surface of the developer drum. At the transfer gap, the toner particles are transferred from the transfer drum onto the developer drum, where they form the second layer. Due to the rotation of the drum, the toner particles of the second layer are conducted past a developing gap between the developer drum and a toner image carrier. The toner image carrier carries a latent charge image onto which toner particles are selectively applied at the development gap, whereby a toner image arises. The toner image is then applied onto an ultimate image carrier, for example onto paper, from the toner image carrier with or without employment of an intermediate image carrier.
What is disadvantageous about the known method is that a monitoring of the developing process and, in particle, of the amount of toner output by the developer unit is not possible. When the toner amount per surface on one of the toner acceptance surfaces or the charge of the toner particles during developing as well lies below or above a predetermined rated value or, respectively, rated range, then the error is not recognized until the finished print image. A reaction thus ensues relatively late. The disturbances in the print image are particularly noticeable given picture elements in the print image that are printed large-area.
In the known method, it is also not possible to exactly set the toner mass per surface section on the toner acceptance surface or the toner charge per surface section, to keep it constant during printing mode and to potentially adapt it to specific print jobs.
Both dry toner as well as liquid toner are employed as toner. Given liquid toners, for example, mechanical devices with electrical auxiliary potential are employed for applying the toner. The toners that are employed can still be divided into a single-component and multi-component toner.
What are understood by electrographic printer are, in particular, electrophotographic printers, ionographic printers and magnetographic printers. It is also known to employ bands on which the toner layer is deposited instead of the developer drum or, respectively, the transfer drum.
The Abstract of Japanese Patent Application JP-A-06067527 explains a developer unit wherein the actual toner mass per surface section of the developer drum is regulated dependent on the sensor signal of a sensor with the assistance of a force field between a transfer drum and a developer drum.
U.S. Pat. No. 5,339,140 explains a developer unit wherein the charge of a toner particle layer on the developer drum is acquired with the assistance of a sensor unit. Dependent on the output signal of the sensor unit, a charging device that is arranged along the toner path is controlled such in a control circuit that the actual toner charge reaches a rated toner charge.
U.S. Pat. No. 5,285,243 explains a developer unit wherein the developing rate is acquired with the assistance of a sensor that acquires the toner mass per surface unit. The charging potential, the illumination, the bias potential or, respectively, the toner concentration is modified dependent on the acquired developing rate.
The Abstract of Japanese Patent Application JP-A-58121050 explains a developer unit with a developer drum. The charge of the toner particles on the developer drum are [sic] acquired with the assistance of a sensor. A charge unit is driven such in a control circuit dependent on the output signal of the sensor that the toner on the developer drum has a predetermined charge or, respectively, a predetermined surface potential.